Hi all,
a little question about external signature.
I have a pdf to sign. I read about this code:
PdfReader reader = new PdfReader("my.pdf");
FileOutputStream fout = new FileOutputStream("my_signed.pdf");
PdfStamper stp = PdfStamper.createSignature(reader, fout, '\0');
PdfSignatureAppearance sap = stp.getSignatureAppearance();
sap.setCrypto(null, new Certificate[]{certificate}, null,
PdfSignatureAppearance.SELF_SIGNED);
sap.setReason("Hello");
sap.setLocation("Italy");
sap.setVisibleSignature(new Rectangle(100, 100, 200, 200), 1, null);
sap.setExternalDigest(new byte[128], new byte[20], null);
sap.preClose();
MessageDigest messageDigest = MessageDigest.getInstance("SHA1");
byte buf[] = new byte[8192];
int n;
InputStream inp = sap.getRangeStream();
while ((n = inp.read(buf)) > 0)
{
messageDigest.update(buf, 0, n);
}
byte hash[] = messageDigest.digest();
String hashFirmato = somehow_signed_hash;
PdfPKCS7 sig = sap.getSigStandard().getSigner();
sig.setExternalDigest(Base64.decode(hashFirmato), null, "RSA");
PdfDictionary dic = new PdfDictionary();
dic.put(PdfName.CONTENTS, new
PdfString(sig.getEncodedPKCS1()).setHexWriting(true));
sap.close(dic);
but I can't use this approach,because I know the certificate used to sign
only after the signature operation.
So I tried this:
PdfReader pdf = new PdfReader("my.pdf");
PdfStamper stp = new PdfStamper(pdf, new FileOutputStream("my2.pdf"));
PdfFormField sig = PdfFormField.createSignature(stp.getWriter());
sig.setWidget(new Rectangle(100, 100, 200, 200), null);
sig.setFlags(PdfAnnotation.FLAGS_PRINT);
sig.put(PdfName.DA, new PdfString("/Helv 0 Tf 0 g"));
sig.setFieldName("Signature1");
sig.setPage(1);
stp.addAnnotation(sig, 1);
stp.close();
MessageDigest messageDigest = MessageDigest.getInstance("SHA1");
byte buf[] = new byte[8192];
int n;
InputStream inp = new FileInputStream("my2.pdf");
while ((n = inp.read(buf)) > 0)
{
messageDigest.update(buf, 0, n);
}
byte hash[] = messageDigest.digest();
Certificate certificate = certificate_obtained_after_signing;
String hashFirmato = signed_hash_obtained_from_external_signature_operation;
PdfReader reader = new PdfReader("my2.pdf");
FileOutputStream fout = new FileOutputStream("my_signed.pdf");
stp = PdfStamper.createSignature(reader, fout, '\0');
PdfSignatureAppearance sap = stp.getSignatureAppearance();
sap.setCrypto(null, new Certificate[]{certificate}, null,
PdfSignatureAppearance.SELF_SIGNED);
sap.setReason("Hello");
sap.setLocation("Italy");
sap.setVisibleSignature("Signature1");
sap.setExternalDigest(new byte[128], new byte[20], null);
sap.preClose();
PdfPKCS7 sig2 = sap.getSigStandard().getSigner();
sig2.setExternalDigest(Base64.decode(hashFirmato), null, "RSA");
PdfDictionary dic = new PdfDictionary();
dic.put(PdfName.CONTENTS, new
PdfString(sig2.getEncodedPKCS1()).setHexWriting(true));
sap.close(dic);
But I obtain an invalid signature.
Any idea?
I would appreciate any hint.
Thanx
--
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